Pulse plating of Pd-Ni alloys: Dependence on current density

Abstract

Pulsed-current electrolysis with the ratio of on-time to off-time of 1:99 has been applied to the deposition of Pd-Ni alloys from a palladium ammine chloride-nickel sulphate bath. The change in the metal ratio of the alloy deposits with an increase in the average current density was less pronounced using the application of pulsed-current electrolysis with extremely short on-time, 0.1 ms. The dependence of the hydrogen content of the Pd-Ni alloys in the current density was also smaller in deposits obtained by the pulsed-current electrolysis with shorter on-time. Even though current density was appreciable, extremely short on-time and much longer off-time brought about no diffusion polarization. The factor affecting the composition of the Pd-Ni alloy deposits (metal ratio and hydrogen content of the films) seemed to be the concentration of the depositable ions in the vicinity of the electrode surface. The preferred orientation of the Pd-Ni alloys deposited by pulsed current changed in the order (111) → (100) → (110) with increase in the current density. The energy required for two-dimensional nucleation on metals with the f.c.c. lattice has been known to increase in the same order. In a similar manner to the deposition of the single metal, an increase in the average current density in the alloy deposition led to a high overpotential and produced fine-grained deposits. The structural features of the Pd-Ni alloy deposits such as the preferred orientation and the grain size seemed to depend on the amount of energy supplied for the crystallization process of the metals.